1. Field of the Invention
The present invention relates generally to mobile units, i.e. autonomous robots and more specifically to a method for collision avoidance with the assistance of a steering angle field for an autonomous mobile unit.
2. Description of the Related Art
Sensor-assisted motion of autonomous mobile units in complex, unknown environments fraught with obstacles such as, for example, offices or dwellings, makes a considerable demand of the control and of the data interpretation of the mobile unit.
Such a unit, for instance a robot, is only capable of carrying out useful tasks when it can move goal-oriented in its environment and can also avoid obstacles over a period of several hours.
Since the area of movement of the unit is usually unknown and also changes dynamically, it is meaningful to locally identify most of the details that affect the immediate movement of the unit. Consistent therewith, a distinction is made between the planning, which supplies a sequence of intermediate target points, and local maneuvering, which moves the autonomous unit from one intermediate target to the next intermediate target. Fast mechanisms that allow obstacles to be reliably avoided and that nonetheless assure great mobility of the unit are required for this task. The unit should be able to move without advance information in unprepared surroundings and should be able to do this with reasonable speed (approximately 50 cm per second). The typical distances between obstacles can thus be on the order of magnitude of the dimensions of the mobile unit or smaller. The passages that it must traverse when travelling can thereby also be extremely tight obstacles (for example, persons) can move with a speed that is comparable to that of the unit. Thus, the self-propelled unit must work most of the time at the limits of its sensor equipment or of its geometrical and kinematic restrictions. An additional complicating factor when ultrasound sensors are utilized is that these have the disadvantage of a near-range blind zone.
The following fundamental works in the field of orientation of autonomously operating mobile units are known: R. Bauer, W. Feiten, G. Lawitzky, Steer Angle Fields:
An Approach to Robust Maneuvering in Cluttered, Unknown Environments, Proc. Int. Workshop on Intelligent Robotic Systems, pp.67-70, July 1993. J. Borenstein, Y. Koren, "Histogrammic In-Motion Mapping for Mobile Robot Obstacle Avoidance", IEEE Trans. on Robotics and Automation, Vol.7, No.4, August 1991.
Despite the comprehensive work in the field of self-propelled mobile units, there are still difficulties in the interpretation of sensor information and in assuring a fast reaction to dynamically changing environments. Another problem is the taking of these changes into consideration in conjunction with a local orientation of autonomous mobile units.